Method of making inside frosted electric lamp bulbs



July 5 1938- 1.. E. cALKxNs ET AL 2,122,512

METHOD OF MAKING INSIDE FROSTED ELECTRIC LAMP BULBS Filed July 29, 19256 2 Sheets-Sheet 1 July 5, 1938. L. E. cALKlNs ET Al. 2,122,512

METHOD OF MAKING INSIDE FROSTED ELECTRIC LAMP BULBS f Filed July 29, 1936 2 Sheets-Sheet 2 Patented July 5, 1938 UNITED STATES PATENT OFFICE METHOD F MAKING INSIDESFROSTED ELECTRIC LAMP BULB y Application July 29, 193s, serai No. 93.246 z claims. (c1. 41'-4,z)I

'I'his invention relates primarily to the inside frosting of electric lamp bulbs, and also to the character of frosted surface produced, whereby such ware has the requisite strength against breakage and the desired brightness reduction with minimum light absorption for commercial Inside frosted lamp bulbs have features of advantage in use over outside frosted or other types of light diffusing bulbs, and a considerable demand has developed in the trade for lamps with such bulbs. In the past, dimculty has arisen in the inside frosting of such bulbs due to the frosting methods ordinarily employed, when applied to the inside of a bulb,eifecting such a weakening of the bulb as to render it fragile for commercial handling. f

It has heretofore been found, however, that if a lamp bulb frosted on the inside in the usual manner is given a second or additional frosting treatment of lower degree than that to which it was first subjected, it becomes sufilciently strong for commercial handling, the strengthening action in such case being supposedly occasioned by the changing of the frosting pits or depressions from sharp angular to rounded form. It is fur- ',ther found, however, that while such treatment 1 when first applied materially strengthens such bulbs against breakage, they weakened with age to such an extent that within a very few months the bulbs in -many cases become so fragile as not to permit commercial handling without breakage.

The primary object of the present invention is the provision of a solution and method for producing, by a single acid or etching treatment, an inside frosted electric lamp bulb of highly eilicient light giving qualities and of suitable strength over a prolonged period for commercial handling, and which does not have rounded etching pits or depressions.

A further object of the invention is thevproduction of an inside frosted electric lamp bulb of a strength suitable for commercial handling and which will, with a minimum of absorption of light, sufficiently diffuse the emitted light of the associated light source as to prevent any objectionable glare, thus giving maximum light emission, increasing the lamp life at designed efficiency and improving the ultimate lamp quality.

In the drawings, Fig. 1 is a more or less diagrammatical side elevation of an apparatus employed in the practicing of our inside bulb frosting method, with parts broken away, and with the bulbs in the first three stages in raised position; Fig. 2 is a similar fragmentary enlarged view of the first three stages of the apparatus with the bulbs in lowered positions in such stages, and Fig. 3 is a reproduction of a photornicrograph enlarged ilve hundred times of the inside 5 frosted surface of a bulb frosted by our method.

The present invention resides (l) in the frosting solution employed; (2) in the method of applying the solution and the subsequent treatment of the bulbs in the inside frosting thereof, l0 and (3) in the bulb itself produced by such method characterized by the form of its inside frosted surface and by the strength and light transmitting qualities of the bulb.

The frosting solution preferably employed may Il be divided into three parts, i. e., A the acid part, containing the acid and acid fiuorides; B the crystalline part, containing the crystalline iluorides, sulphates and water, and C the binder part, containing molasses for increasing- 20 the consistency of the compound and giving it the requisite viscosity.

(A) Part A preferably comprises the following ingredients in substantially the proportions noted: A 25 Ammonium acid fluoride 33 lbs.3oz. Hydrofluoric acid (approximately 10 liters These materials are put into a drum of rubber, or 30 other suitable acid resisting material, and rolled or agitated until complete solution takes place.

(B) Part B preferably comprises the following ingredients in `substantially the proportions noted:

V 35 Sodium acid sulphate 11 lbs. 1 oz. Sodium fluoride 111bs. 1oz. Water- 6 liters These ingredients are put into a rubber mill preferably containing bronze balls. This mate- 40 rial is milled usually for at least three hours, or until it contains no lumps or unground materials.

` At the beginning of the run, pressure is generated Molasses l2 liters A commercial grade of molasses is used. 'I'he presence of the molasses in the solution retards 55 the ow of the liquid by acting as a binder, and also retards, due to its viscosity, the rate of. re-

action of the solution. The change of viscosity.

of the molasses with temperature allows an easy method of controlling the etching action, and this is obtained by the application of heat to the outside of the bulb during the etching operation, as hereinafter described. lt is found. that by applying water to the outside. of a bulb during the etching operatic-n and by varying the time, the flow and temperature of the water, the formation of t`ne crystalline structure of the etched surface can be controlled.

When part B has been sufllciently miiled, part A is added thereto and the whole yis then preferably milled for at least half an hour or until a thorough mixing has taken place. This mixture is then turned into a wooden tuband part C added, stirring well while adding. The solution which is now ready for use has a light brown creamy appearance and a consistency substantially equal to No. 10 motor oil.

The sodium uoride contained in part B oontrols more or less the crystalline structure by stabilizing the viscosity of the solution. The sodium fluoride does not dissolve to any great extent and the fine particles thereof in su'spension in the solution form nuclei for crystal formation of ammonium, sodium-and calcium silica fluorides (or uosilicates). 'I'his crystalline structure is quite important in obtaining the desired strength characteristics of an inside frosted bulb.

There is also another use for the sodium fluoride in the solution. When sodium acid sulphate is `mixed with sodium. fluoride in aqueous solution, an exothermic reactie-n takes place, causing heat to begiven off. This reaction forms some free sulphuric acid, sodium sulphate, hydroiiuoric acid and sodium acid fluoride along with sodium acid sulphate and vsodium fluoride. All these substances. are in a state of delicate chemical v balance, and it is believed that this equilibrium tends to stabilize the concentration of acid, sodium fluoride, sodium acid iiuoride and sulphates in solution. In order to prove our contentions in this respect, the concentrations of sodium acid sulphate were varied. It was found that the addition of only 1% more of sodium acid sul-l phate to the solution completely changed the properties of the frost. The matt became coarse and could not be easily controlled. When less sodium acid, sulphate was added, the frost was not heavy enough and was too fine in crystalline structure to properly diff-ese light.

v'lng of alamp bulb, `the frosting-solution rabove j nsv It is found that part B, when used alone, will etch the glass, but the reaction is too slow for comercial use, dueto the low hydrouoric acid content. When, however, parts A and B are thoroughly mixed together and part C added, a powerful frosting solution is obtained and one which, when use-ci in connection with the method hereinafter described, -will produce an inside frosted bulb which is suniciently strong against breakage `to permit ordinary commercial handling, will effecta proper diffusion of light emittedtherefrom to prevent objectionable' glare or brightness, 'and will have a greater lumen output with consequent higherinitial rating than other inside frosted bulbs now aware'. y

In practicing our invention in the inside frostmade of which we are described is first vapplied in stream or jet form under low pressurel (about 11/2 to 2 lbs.) up into the interior of the bulb, so that the stream strikes the centralutopclosed portion of the bulb, flows evenly down the sides and discharges from its lower openv end The solution is applied over a period of about ten seconds.

Immediately following the application of the acid the bulb is. subjected to an external hot water treatment to control the etching action of the acid adhering to the inner surface of the bulb. Hot water is caused to iiow onto and down around the closed end of the bulb discharging from its lower end, and the temperature of the water and time applied are important items in the etching operation in controlling the degree of etching and consequent crystalline structure of the frost surface to produce the desired results. The temperature of the water preferably should be approximately 63 C., and the water should be of sumcient quantity to completely cover the bulb. The time of application varies, depending on the bulb size, but for moet sizes the time is about ten seconds.

'I'he bulb is next subjected to a thorough internal washing to entirely remove the etching acid therefrom and thus stop any further etching action. This` washing is preferably accomplished by discharging a stream of water under relatively high pressure (about 15 lbs.) up into a bulb from a rather small orifice (about 115th of an inch in diameter). For most satisfactory results the temperature of the water should be from 50c to 95 C.

After washing, the bulb is thoroughly dried preferably by directing hot air thereagainst, both inside and outside, and is then ready for use in a lamp. The buib may also be held over a. flame to facilitate drying. Nothing new is claimed for the washing and drying operations.

An apparatus for practicing the invention is illustrated in Figs. 1 and 2, and includessuccessively arranged means for imparting the successive treating steps above described together with means for directing the movement of trays of bulbs successively from one position to another in the frosting rnethod.

'I'he bulbs l to be frosted are mounted in convenient numbers in trays 2 and such trays are moved from end to end of the apparatus along laterally spaced guide rails 3, in the present instance of angle iron. IThe rails are divided into a rear section A and a front section B, the rear section being vertically movable and mounted for such purpose on uprights 4 resting at their lower ends on lever arms 5, whereby a rocking of such arms effects a predetermined raising or lowering of the trays on such section. Disposed under the movable section Aare the acidapplying unit C, the etching control unit D, and the washing unit E of the apparatus.

A'I'heacid applying unit C, es illustrated, includes a tank 6 divided by a horizontal partition 1 into a lower compartment 8 for the frosting solution and an upper drainage compartment 9, which latter has communication with the ilrst compartment through one or more drainage tubes Il),l each provided with an outwardly opening check-valve. Air under controlled pressure is supplied'to the compartment 8 through a conduit Il, 'anda solution agitating means I2 is provided in the bottom portion of the compartment. A so- Ylution:dischargej tube i3 extends upwardly from its uppe'rend in `a restricted discharge nozzle in central vertical register with the lower open end v of a respective bulb I in the superposedtray 2,

one tube being provided for each bulb in the tray. The discharge orlilce of each tube is preferably about one-quarter inch in diameter. A drainage funnel Il is provided through the top. of the compartment 9 in free surrounding relation to each tube nozzle and has its upper flared mouth end of suitable size to freely receive the lower end of a registering bulb when in lowered solution receiving position, as shown in Fig. 2. 'I'he bulbs in the first tray 2 being lowered into receiving relation to the discharge tubes Il, the controlled air pressure of approximately one and one-half to two pounds yfrom the line I I is turned into the solution compartment 8 andthe solution thereby forced up through the several discharge tubes into the registering bulbs I, striking the top portions of the bulbs, flowing down the sides thereof in entirely covering relation to the inner surfaces of the bulbs and discharging from the open lower ends of the bulbs around the respective discharge tube nozzle into the registering drainage members I4. 'Ihe solution passes from the members Il into the drainage compartment 9 and thence returns through the drainage tube I to the compartment 8.

Withthe present apparatus, in which a comparatively small capacity solution tank 8 is employed, the bulbs are subjected to three successive shots of the solution instead of one continuous shot, inasmuch as the solution is not returned to the tank as rapidly as it is discharged under pressure through the tubes I3, so that the small quantity of solution in the tank would be exhausted before the completion of the single operation. The solution is discharged into the bulbs for a total period of about ten seconds, and it is found that the results are the same if the discharge is single or divided into several shots. By utilizing three shots, each of about two seconds duration, suilicient time elapses between shots for the return solution to replenish the tank supply to take care of the next shot.

When the application of the acid to the bulbs has thus been completed, the tray of bulbs is moved to the next position D where water is discharged onto the tops of the bulbs from an overhead supply means Ii. The water thus discharged passes down around the bulbs in complete enveloping relation thereto and discharges from their lower ends into a drainage tank I6. The trays have their bottoms sumclently open to permit the free drainage of the water therethrough around the bulbs. The temperature of the water is approximately -63" C. and the discharge is for approximately ten seconds. If the temperature is reduced the time is increased, and vice versa. The applying of the solution to the interior of the bulb and the external hot water treatment could both be effected in one position, except for the drainage Water getting into the solution.'

After the water treatment at position D, the trays are advanced to position E where hot washlng water is discharged into the bulbs through discharge pipes I8 and drained back therefrom through funnel members I9 in substantially the same manner as in handling the solution in position C. The washing water is preferably discharged at a pressure of about fteen pounds,

and the best results are obtained by having the temperature ofthe water from 50 to 95 C. 'Ihis same washing operation takes place at two successive stages of advancing movement of the trays along the apparatus, so as to effect a thorough washing of the bulbs and to permit the washing operation to consume approximately twice the time of each of the preceding operations.

After the washing operation, the trays are ad- .vanced step by step through a drying oven 20 in which hot air is circulated around the bulbs and in the bottom of which is provided a gas burner or other flame discharging means 2| to apply heat to the lower open ends of the bulbs. As the trays of bulbs advance along the apparatus, they may be subjected to a further drying action by the discharge of hot air thereto from'a conduit 22.

It is found that the above method, combined with a frosting solution substantially as above described, produces an inside frosted lamp bulb which is sumciently strong against impact to permit ordinary commercial handling without breaklng, and also that while a lamp bulb frosted by our method will have proper light diffusing qualities its percentage of light absorption isexcep- :lilcirally low and its lumen output exceptionally All strength tests referred to herein were made on an ordinary type of bump tester such as shown and described in the Plpkin Patent No. 1,687,510, and it is found that inside frosted bulbs which show an impact strength of 7 or more on such tester, when made up into lamps, are sumciently strong for commercial use.

The following strength readings indicate for each set the average bump tester breakage point for twenty clear bulbs taken at random from regular stock and also for twenty bulbs inside frosted by our method and taken at random, from stock:

` The average shown for each of the above vertical sets of ilgures is 57.5 for the clear bulbs; 12.3 for the inside frosted bulbs, and 21.7 for the percentage of strength of inside frosted bulbs to clear bulbs.

If, therefore, the average strength of clear bulbs to reduce breakage by impact is 57.5, and the average minimum commercial strength requirement for inside frosted bulbs is 7, then it is apparent that inside frosted bulbs to resist breakage by impact should have an average strength of 12.15% of that of the clear bulb average.

Lumen output readings for clear bulbs as compared to inside frosted bulbs of the same types and wattages and the percentage of one to the other are as follows:

In making the above lumen output tests, twelve bulbs were used in each of the tests and were taken at random from regular stock of the same make of clear and frosted bulbs, respectively, the

frosted bulbs before frosting being as nearly like the clear bulbs as possible to obtain.

The frosted surface produced by our method is of crystalline structure and has sharp angularrv f crests and crevices and is characterized mainlyin its difference over ordinary single treatment 'that when such formation is absent the bulbs in general are too fragile for commercial handling. The frosted surface produced by our method is further characterized and distinguished from the frosted surface produced by the double treatment method described in United States Patent No. 1,687,510 to Pipkin by the absence of rounded crevices. the presence of which in the inside frosted surfaces of lamp bulbs has heretofore been considered necessary to produce the requlsite strength in the bulb to prevent breakage under ordinary commercial handling. k

Having thus described our invention, what we claim as new, and desire to secure by United States Letters Patent, is:

1. The method of inside frostingthin hollow glassware such as lamp bulbs, which consists flowing a glass etching solution into and v over the linterior surface ofthe ware,andcontrolling the iilow oi' the fluid yby, the addition of molasses thereto, and thenflowirigjfaznlm of hot water over the exterior of thewa'r'eto control'the etching action.

2.` The method of' inside frosting thin hollow.

glassware such as lamp bulbs, which consists in injecting-three successive shots of a glass etching fluid, each for approximately two seconds, against the interior ofthe-ware ina position to flow down over all oflthesu'rface to be etched, said solution containing the following ingredients inl approximately the proportions namedl Ammonium vacid uoride' 33 lbs. 3 oz.

flowing water lat ,approximately"63"v C. over the exterior of` the surface for approximately the same length of time that the etching fluid is flowing over the interior of the surface and therevafter washing out the interior of the surface with fluid under a higher pressure than that at which the etching fluid is impinged upon the 4interior of the'ware. K

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